The present invention relates to techniques for making soldering iron tips having protective outer layers, and the tips produced thereby,
Manufacturers of soldering irons (as well as desoldering irons) typically use copper (Cu) or copper-based materials for the tip of the soldering iron. Copper offers high thermal conductivity at relatively low cost. Moreover, copper can be readily machined into the desired tip geometry. For example, FIG. 1 illustrates an exemplary tip 1 formed by machining a monolithic rod of copper or a copper alloy. 2.
However, copper tips also have a number of undesirable properties. When heated to the high temperatures required for soldering, the tips may dissolve in the solder and/or corrode in air. Furthermore, the tips may deform when mechanical pressure is applied thereto. For this reason, simple copper-based soldering tips have a relatively low tip life.
The prior art has addressed this problem by coating the copper tips with one or more outer layers. More specifically, as illustrated in FIG. 2, the end of the tapered portion of the tip 1 (referred to as the xe2x80x9cworking areaxe2x80x9d) is coated with an outer layer 4 of iron (Fe). The iron coating 4 protects the softer copper core 2 from deformation during soldering operations, and from dissolving in the solder. Iron is also readily wettable by molten solder. The remainder of the soldering iron tip 1 is covered by other types of materials 6, such as a layer of chromium (Cr) or a layer of chromium formed over a layer of nickel (Ni). These layers 6 provide a good electrical connection between the tip of the soldering iron and ground, thus ensuring a low tip-to-ground voltage potential and resistance. These layers 6 also protect the copper 2 from corroding in air. Furthermore, chromium offers poor wettability by the solder and thereby prevents the solder from creeping up the tip from the working area and degrading the performance of the soldering iron tip.
Typically, these materials are coated onto the copper tip by a deposition technique known as electroless plating or electroplating. Electroplating involves applying a voltage between the soldering iron tip (cathode), and pieces of the metal to be deposited (the anode), through an acid-based aqueous electrolyte. The soldering iron tip and the metal anode are both submersed in the electrolyte. The applied voltage causes metal ions to flow from the anode to the cathode (soldering iron tip) through the electrolyte, thus depositing the metal onto the tip of the soldering iron in a controlled fashion. For example, U.S. Pat. No. 3,315,350 proposes a technique for electroplating a layer of iron on a copper tip, and then electroplating an additional layer of nickel and chromium on the iron layer. U.S. Pat. No. 3,986,653 proposes electroplating an outer layer of osmium or ruthenium (or an alloy thereof) on a soldering iron tip.
Electroplating of copper soldering iron tips has disadvantages. First, electroplating sometimes produces a coating of uneven thickness on the tip, especially at regions where the contour of the tip abruptly changes. Second, the process itself is inherently unstable, resulting in differences in plating thickness and quality from one production batch to the next. Third, electroplating is relatively expensive, which is partially due to the large amount of manual labor required by the technique, and the need to dispose of the chemical solutions used in the process in an environmentally safe manner.
For these reasons, some manufacturers have looked to alternative ways of constructing tips having hardened outer layers. For example, U.S. Pat. No. 4,055,744 discloses a technique for forming a hardened outer layer on the working area of a soldering tip by separately forming an iron cap, and then mechanically crimping the cap onto the soldering iron tip. The composite structure of the cap and the tip is further shaped by manually hammering the composite structure, or by using a swaging machine. While avoiding the problems associated with electroplating, crimping the cap to the copper tip may tightly bind the cap to the tip only at selective locations of the tip, such as at the base of the tip, thereby reducing the contact area between the tip and the cap. This, in turn, may reduce the transfer of heat from the tip to the cap, thus reducing the performance or the efficiency of the soldering iron.
Another problem addressed by the present invention pertains to soldering irons which include xe2x80x9cheaterxe2x80x9d elements. As illustrated in FIGS. 3 and 4, a heater 8 is the component of the soldering iron which actually generates heat. That is, the electrical coils of the soldering iron (not shown) transfer energy to the heater 8, which in turn transfers heat to the working area of the soldering iron tip 1. In one tip design produced by the assignee of the present invention, the heater 8 element comprises a clad wire segment having an inner core 12 and an outer layer 10 formed thereon. The heater element 8 is press fit into a machined hole 14 located in the back of the tip 1. The mechanical interface 16 (in FIG. 4) between the heater 8 and the tip 1 impedes the transfer of heat from the heater 8 to the tip 1.
It is therefore an exemplary objective of the present invention to provide a technique for making soldering iron tips that facilitates efficient and reliable large-scale production of the tips, preferably without the use of electroplating. It is a further exemplary objective of the present invention to provide a technique for making soldering iron tips which does not impose interfaces which impede the flow of heat from the heater to the tip.
These and other exemplary advantageous features are achieved according to a first aspect of the invention which entails producing a tip from a clad wire segment. The technique entails cutting a length of clad wire into a plurality of segments, where each segment comprises a core of material (such as copper) and an outer protective layer (such as stainless steel, nickel of high purity, chromium of high purity, Fexe2x80x94Ni alloys such as Invar-type alloys, or other suitable material). Each clad wire segment is then shaped into a soldering iron tip by a cold heading process, or other metal forming process. In the finished tip, the outer protective layer is disposed xe2x80x9cbehindxe2x80x9d the working area of the tip, and provides good electrical conductivity between the tip and ground, thus maintaining a low tip-to-ground voltage potential and resistance. The outer layer also protects the inner core (of copper) from oxidation, and offers poor wettability, which prevents solder from adhering thereto.
According to another aspect of the invention, the clad wire segment can be further shaped to form an integrated heater element located on one end of the tip. Since the heater element is formed from the same segment of the clad wire segment as the tip itself, this technique ensures metallurgical continuity between the heater and the working area of the tip, and thereby improves the transfer of heat between the heater and the tip by eliminating the mechanical interface 16 shown in FIG. 4.
According to another aspect of the invention, the above described metal forming steps can be performed on a wire (or rod) segment which does not include a protective outer layer.
According to still another aspect of the invention, a protective outer layer for the working area of the soldering iron tip can be formed by inserting a separately formed cap of iron (or like material) over the working area portion of the tip. More specifically, the technique entails producing a thin strip or sheet of protective layer material, such as iron. Tapered caps are then stamped out of the sheet using a die having a shape which resembles the shape of the soldering iron tip. The caps formed in this manner are then inserted over the working area of the soldering iron tips, and attached thereto by applying brazing material to the caps or the tips and then melting or sintering the brazing material. Alternatively, the brazing material can be applied directly to the strip of material (before stamping is performed) to further expedite the manufacturing process. In either event, the use of brazing, or like technique, improves the thermal conductivity between the tip and the cap by creating an intimate metallurgical bond between the tip and the cap, as compared with the prior art technique of crimping the cap to the tip.
According to another aspect of the present invention, a clad wire or rod segment is used to form a soldering tip including one or more protective outer layers on the working area of the soldering tip.